In a Linux environment OpenSSL provides an easy way to un-encrypt this:

openssl rsa -in server.key.secure -out server.key

Make sure to replace “server.key.secure” with the filename of your encrypted key, and “server.key” with whatever you want the un-encrypted filename to be. If you are prompted for a passphrase whoever made the key specified one. Unfortunately you will not be able to decrypt the key without the correct passphrase.